In general, purification treatment such as dialysis treatment, a blood circuit route consisting of flexible tubing is used to place the blood of patient in extracorporeal circulation. This blood circuit route arrangement mainly includes an arterial blood circuit route having an arterial needle at one end to collect blood from the patient and a venous blood circuit route having a venous needle at the other end to return the blood to the patient. A dialyzer between the arterial blood circuit route and the venous blood circuit route purifies the blood circulating extracorporeally.
Such a dialyzer includes plural hollow fibers in the inside of dialyzer. Blood flows in each inside hollow fiber and dialysis fluid flows outside the hollow fibers (i.e. between external surface face of the hollow fiber and inside surface face of the dialysis device case). The hollow fiber is a blood purification membrane with small pores on its surface. Wastes in the blood flowing in the inside of hollow fiber are discharged into the dialysis fluid after passing through the blood purification membrane, and the blood, of which wastes are discharged for purification, returns to the patient. Also a ultrafiltration pump installed in the inside of the dialysis device removes water from patient's blood while dialyzing the patient.
When, for instance, the arterial needle and the venous needle are punctured to the shunt (a connected part of an artery and a vein by a surgical operation) and its periphery to circulate the blood extracorporeally, a blood-recirculation takes place by which the blood purified and returned to the patient from the venous needle is collected from the arterial needle without passing trough patient's organs. Such blood-recirculation is not desirable because the purified blood is again extracorporeally circulated and, as a result, the volume of extracorporeal blood-circulation required to be purified is decreased so that purification efficiency is lowered.
A blood purification device (e.g. JP Patent Published 2000-502940) has been disclosed, in which blood-recirculation could be measured using a specific peak, as a benchmark, assigned within a variation of concentration of blood extracorporeally circulating by driving a ultrafiltration pump rapidly in a short period of time. Referring to the patent published, in the dialysis device disclosed, a sensor measuring blood concentration (hemoglobin concentration) was installed in the arterial blood circuit route and a recirculation of blood during dialysis treatment was determined with a specific peak detected by such as a sensor.